Method of fabricating semiconductor device

A method of fabricating a semiconductor memory device, comprising:

• forming mask patterns on a semiconductor substrate;
• forming trenches defining active regions by anisotropic etching of the semiconductor substrate using the mask patterns as an etch mask;
• removing the mask patterns to expose the active regions;
• sequentially forming a thermal oxide layer and a liner layer covering upper portions of the active regions and inner walls of the trenches on the resulting structure in which the upper portions of the active regions are exposed;
• forming a device isolation layer filling the trenches on the liner layer;
• etching the device isolation layer to expose an upper surface of the liner layer and to form device isolation patterns filling the trenches;
• dry etching the liner layer to expose the upper portion of the thermal oxide layer at the upper portions of the active regions;
• etching the exposed thermal oxide layer to expose the upper portions of the active regions;
• and
• forming a gate oxide layer on the exposed upper portions of the active regions.